Predictable Method for Reducing Power Consumption during Peak Demand

ABSTRACT

System and method for reducing electricity consumption during peak demand period is disclosed. The power distribution system comprises a power grid, a control unit and a plurality of consumption units. The consumption unit further comprises a power limiter. The control unit sends instructions through a communication network to consumption units to activate the power limiters. Power consumptions for appliances in the units are then adjusted to meet the power limitation. Implementations of AC and DC power limiters are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable

BACKGROUND 1. Field of Invention

This invention relates to a power distribution system, specifically to apower distribution system including a means of reducing peak demand.

2. Description of Prior Art

A utility distributes electricity to consumption units such asresidential and commercial units through power grids and sub-grids. Theconsumption units do not always consume power at a constant rate. Insome instances, the utility may experience periods of peak power demandthat are greater than the average power demand. In order to satisfy thepower demand during periods of peak demand, the utility may operate ator near to maximum capacity, it may operate supplemental generators,and/or it may purchase electricity from other sources. When theelectrical distribution system runs near capacity, there is a potentialthat the system may fail, and operating supplemental generators andpurchasing electricity from other sources may increase the utility'soperating costs and may have a significant negative environmentalimpact.

As a result, methods have been adopted by utility to discourage powerconsumption during peak demand period. The utility may charge aconsumption unit a premium for peak electricity demand. For example, thepremium may take a form of higher average rates and/or additionalcharges based on the consumer's peak demand. Effectiveness of such anapproach depends largely on awareness of consumers on the price andtheir willingness to take appropriately actions and is essentiallyunpredictable.

It is desirable to have a predictable method for reducing the peakdemand of the power consumptions.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide apredictable method for managing peak power demand by limiting powerconsumptions in selected consumption units.

It is another object of the present invention to provide programmablepower limiters that are suitable to be implemented in the residentialand commercial units.

It is yet another object of the present invention to provide a controland communication method for controlling the peak power demand of apower distribution system.

The power distribution system comprises a power grid, a control unit andmany consumption units. The consumption unit further comprises a powerlimiter. The control unit sends instructions through a communicationnetwork to a group of selected consumption units during peak demandperiod. The selected consumption units may have agreements with theutility to limit the power consumption during peak demand period. Afterreceiving the instructions, the consumption units activate the powerlimiters. Power consumptions for appliances in the units are adjustedaccording to predetermined rules to meet the power limitation.

According to one embodiment, the power limiter is implemented in ACpower domain. According to another embodiment, the power limiter isimplemented in DC power domain.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsvarious embodiments, and the advantages thereof, reference is now madeto the following description taken in conjunction with the accompanyingdrawings.

FIG. 1 shows, in a schematic diagram, an exemplary power distributionsystem.

FIG. 2 shows, in a flowchart, a predictable method of limiting peakpower demand.

FIG. 3 shows, in a schematic diagram, an exemplary implementation of anAC power limiter.

FIG. 4 shows, in a schematic diagram, an exemplary implementation of aDC power limiter with AC power source.

FIG. 5 shows, in a schematic diagram, an exemplary implementation of aDC power limiter with DC power source.

DETAILED DESCRIPTION

The present invention will now be described in detail with references toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps have notbeen described in detail in order not to unnecessarily obscure thepresent invention.

FIG. 1 is a schematic diagram of an exemplary power distribution system.System 100 comprises a power grid 102. Control unit 104 of a utilitycontrols operation of power distribution system 100. Control unit 104further comprises controller 106, file storage 108 and communicationunit 110. Control unit 104 may be one or more computing systems.

System 100 further comprises multiple consumption units. The consumptionunits may be residential units or commercial units or be any unit thatconsumes electricity drawn from power grid 102. An exemplary consumptionunit 112 is shown in FIG. 1. Consumption unit 112 comprises powermanagement device 114 and appliances 122. Appliances are apparatus thatconsume electrical power. Appliances include but are not limited torefrigerators, air-conditioners, TV systems, computers, lamps and HiFiaudio systems. For a commercial unit, appliances may include productionequipments. Consumption unit 112 may include many different types ofappliances.

Power management device 114 further comprises controller 116, powerlimiter 118 and communication unit 120. Controller 116 may be acomputing system. Power limiter 118 is a device that limits the maximumpower consumption of consumption unit 112. Power limiter 118 may becontrolled by controller 116. The maximum power may be changeable asprogrammed by controller 116. Power limiter 118 is in a sleep modebefore it is activated by controller 116. Communication unit 120 andcommunication unit 110 may form a communication network.

An instruction for limiting power consumption may be initiated bycontroller 106 when a peak demand period is encountered or isanticipated. Controller 106 retrieves a pre-stored agreement withconsumption unit 112 and determines a maximum power consumption value.Communication unit 110 transmits an instruction to the communicationunit 120. After receiving the instruction, controller 116 activatespower limiter 118 to limit power consumption of consumption unit 112. Asa result, some of appliances 122 may be switched off, some may beoperated in a reduced power mode and some may not be allowed to beswitched on if they are being switched off.

Units 110 and 120 may form an ad hoc communication network including butnot limited to 1) a Bluetooth (IEEE 802.15.1) type of network; 2) aZigBee (IEEE 802.15.4) type of network; and 3) a Wi-Fi (IEEE 802.11)type of network. Units 110 and 120 may also be connected to the Internetor to a telephone network. Units 110 and 120 may also be a part of acommunication network conforming to a Power Line Communication protocol.Power Line Communication or Power Line Carrier (PLC), also known asPower Line Digital Subscriber Line (PDSL) is a system for carrying dataon a conductor also used for electrical power transmission.

Power limiter 118 may be implemented in AC or in DC power domain.Present inventive concept does not limit types or scopes of the powerlimiters. Any implementation of the power limiting concept will fit intothe present inventive concept.

FIG. 2 is a flowchart illustrating exemplarily the predictable method(200) of managing the peak power demand. Control unit 104 monitorssupply and demand of power grid 102 continuously (202). If a powershortage situation is encountered or is anticipated as a result of suchas peak demand period (204), instructions will be sent from control unit104 to the selected consumption units 112 through a communicationnetwork (206).

The selected units may have pre-agreements with the utility through acommercial agreement for accepting power consumption limitation duringthe peak demand period. There may be various implementations of suchcommercial agreements that include but are not limited to: (1) a pricediscount for total electricity bill; (2) a credit for consuming apredetermined amount of electricity at a discounted rate at a low powerconsumption period; and (3) free or at a discount for consuming theelectricity power with the accepted limit during the peak demand period.The agreements may be established through an auction. The auction mayutilize the communication network. The auction may also use theInternet. Consumers of the consumption units may place a bid through thecommunication network. Auction results including identities and theagreed maximum electricity values for the consumption units may bestored in a file storage unit of the control unit.

Power management device 114 receives the instruction throughcommunication unit 120 (208). As a result, controller 116 activatespower limiter 118 to limit the maximum power consumption of the unit.Controller 116 adjusts power consumption of various appliances accordingto a program stored in a storage unit of controller 116 (210).Controller 116 may switch off one or more appliances. Controller 116 mayalso reduce power consumptions of one or more appliances (e.g. increasesetting temperature of an air conditioner during summer peak hours).Controller 116 may deactivate power limiter 118 after receiving anotherinstruction from control unit 104 that the power limitation requirementis expired.

FIG. 3 is an exemplary power limiter implemented in AC power domainbased upon an integrated circuit for measurements of thermal signalscomprising a thermal feedback loop.

Such an implementation is known from an article by Pan (the presentinventor) and Huijsing in Electronic Letters 24 (1988), 542-543. Thiscircuit is theoretically appropriate for measuring physical quantitiessuch as speed of flow, pressure, IR-radiation, or effective value ofelectrical voltage or current (RMS), the influence of the quantitygrated integrated circuit (chip) to its environment being determined inthese cases. In these measurements, a signal conversion takes placetwice: from physical (speed of flow, pressure, IR-radiation or RMSvalue) to the thermal domain, and from the thermal to the electricaldomain.

This known semiconductor circuit theoretically consists of a heatingelement, integrated in the circuit, and a temperature sensor. The powerdissipated in the heating element is measured with the help of anintegrated amplifier unit, an amplifier with a positive feedback loopbeing used, because of which the temperature oscillates around aconstant value with small amplitude. In the known circuit thetemperature will oscillate in a natural way because of the existence ofa finite transfer time of the heating element and the temperature sensorwith a high amplifier-factor.

FIG. 3 shows a novel implementation of the thermal feedback principle asmentioned above to AC power limiter 300. AC power limiter 300 comprisesa transformer 302 including primary winding 302A and secondary winding302B. Transformer 302 converts AC power with high amplitude in primarywinding 302A to AC power with low amplitude in secondary winding 302Bwhile maintaining the power almost constant. AC Power sensor 304 coupledto secondary winding 302B receives a portion of AC power proportionally.Power sensor 304 may further comprise a current sensor and/or a voltagesensor. The received AC power is further coupled to power to heatconverter 306 that may include a heating element. The heating elementmay be a heating resistor in an exemplary case. The heating element mayalso be an active component. Power to heat converter 306 (heatingelement) may be a part of an integrated circuit or a chip. According toa different implementation, a rectifier (not shown in FIG. 3) may beused to convert the AC power into DC power before it is used to heat theheating element.

Temperature sensor 308 in the same integrated circuit is used to measurethe temperature of the integrated circuit (chip). According to oneimplementation of the present invention the heating element andtemperature sensor may be placed in a microstructure such as a membraneor a cantilever beam, manufactured by a micromachining technology.

Output of temperature sensor 308 is coupled to one input of comparator310. Reference generated by controller 312 is coupled to another inputof comparator 310. Output of comparator 310, which is a Pulse-WidthModulation (PWM) signal, is coupled to switch 314 that is connected tosecondary winding 302B of transformer 302 to form a positive feedbackloop. Switch 314 may be implemented in various forms as known in theart. Switch 314 maybe a power Metal Oxide Semiconductor Field EffectTransistor (MOSFET) according to an implementation. Switch 314 may be abipolar transistor according to another implementation. Switch 314 mayeven be a Light

Emitting Diode (LED) and a photo detector. The output of comparator 310may be used to drive the LED to emit light that will be detected by thephoto detector. As soon as the measured temperature by temperaturesensor 308 exceeds a predetermined value, set by the reference, theoutput of the comparator switches off switch 314. As a result, powersensor 304 receives no power from secondary winding 302B and the outputof temperature sensor 308 starts to drop. As soon as the output is belowthe reference, the output of comparator 310 switches on switch 314 andtherefore secondary winding 302B. The temperature of the chip or themicrostructure will oscillate around a small value. The output power ofsecondary winding 302B will remain as a constant in a sine wave formmodulated by the PWM signals. The output power of transformer 302 islimited by the duty cycle of the PWM signal. The output power may bedelivered to appliances 122 of consumption unit 112.

The maximum output power of transformer 302 is determined by thereference that sets a level of temperature that the chip or themicrostructure will oscillate around. To sustain a higher temperature,the power sensor will need to draw more power from the secondary winding302B. The reference is determined by controller 312 that receives theinstructions from control unit 104. In an unlimited power operationmode, controller may 312 my set the reference to a sufficiently highlevel to maintain switch 314 in an “on” state.

It should be noted that the temperature level of the microstructure orthe chip also depends on ambient temperature. At a lower ambienttemperature, it requires more power to heat the heating element tomaintain the temperature to oscillate around the predetermined level. Ata higher ambient temperature, less power is required. In one aspect ofthe present invention, an ambient temperature sensor 316 is used tomeasure the ambient temperature. The measurement results are sent tocontroller 312. Controller 312 determines the reference based upon notonly the instructions from control unit 104 but also the ambienttemperature measured by temperature sensor 316. Temperature sensor 316may be a sensor independent of the integrated circuit or the chip.Temperature sensor 316 may also be a part of the integrated circuit orthe chip that will require an appropriate thermal isolation betweentemperature sensor 306 and temperature sensor 316. Such thermalisolation techniques are known in the art.

According to another implementation, system 300 may further comprise anelectricity meter 318 as an option although inclusion of 3118 is notessential for its operations. Electricity meter 318 provides anindependent means of measuring the output power of transformer 302.Controller 312 receives output of electricity meter 318 and adjustsaccordingly the reference to meet the power consumption limitation setby control unit 104. Electricity meter 318 is an electronic meter in apreferred form.

There may be different implementations of integration level of system300. At a minimum level, 306 and 308 are integrated in a single chip orin a single microstructure. At a higher level, 310 may also beintegrated (e.g. 306, 308 and 310 in a single chip). At even higherlevels, 312 and 314 may also be integrated (e.g. 306, 308, 310, 312 and314 in a single chip). At still higher level, 316 and 318 may also beintegrated (e.g. 306, 308, 310, 312, 314, 316 and 318 in a single chip).All such variations shall fall within scope of inventive concepts of thepresent invention.

FIG. 4 shows an exemplary power limiter implemented in DC power domainwith AC power source. System 400 comprises AC/DC converter 320 thatconverts output power of transformer 302 from AC form into DC form.Block 322 modulates the DC power by PWM signal 311. DC power sensor 323is coupled to Block 322 to draw a portion of DC power proportionally.Block 322 delivers output power 321 in PWM form. The DC power receivedby DC power sensor 323 is coupled to power to heat converter (heatingelement) 306. Temperature sensor 308 measures temperature of themicrostructure (chip) that includes the heating element. Comparator 310takes one input from the output of temperature sensor 308 and takesanother input from a reference generated from controller 312. Output ofcomparator 310 in PWM form (311) is coupled to block 322 to modulate theDC power. The temperature of the chip will oscillate around a smallvalue set by the reference. Block 322 converts output of AC/DC converter320 into DC power in PWM form. The output power of block 322 istherefore determined by duty cycle of the PWM signal while the amplitudeis kept constant. The output power of block 322 may be further processedinto DC and/or AC powers before it is delivered to appliances.

Controller 212 is coupled to ambient temperature sensor 216 andelectricity meter 216. Functionalities of 216 and 218 are similar toones that have been described previously in the AC power limitersession.

FIG. 5 shows an exemplary power limiter implemented in DC power domainwith DC power source 324. Power limiter 500 is the same as power limiter400 except that transformer 302 and AC.DC converter 320 are replaced bythe DC power source 324.

While the invention has been disclosed with respect to a limited numberof embodiments, numerous modifications and variations will beappreciated by those skilled in the art. Additionally, although theinvention has been described particularly with respect to reducing powerconsumption of a power grid during peak demand period, it should beunderstood that the inventive concepts disclosed herein are alsogenerally applicable to other power shortage situations including butnot limited to shutdown of power generators because of accidents,natural disasters and terrorist attacks. The inventive concepts are alsoapplicable to other power distribution systems such as micro-grids andpower systems formed by alternative power sources. The present inventiveconcepts are applicable to any implementation of power limiters. It isintended that all such variations and modifications fall within thescope of the following claims:

1. A method of optimizing power consumption of a power grid including aplurality of power consumption units, the method comprising: (a) sendinginstructions from a control unit of the power grid to preselectedconsumption units through a communication network; (b) receiving theinstructions by power management devices in the consumption units; (c)activating a power limiter by a controller of the power managementdevice to limit power consumption in each of the preselected consumptionunits; and (d) adjusting power consumptions of a plurality of appliancesin each of the preselected consumption units according to predeterminedrules.
 2. The method as recited in claim 1, wherein said method furthercomprising deactivating said power limiter after receiving furtherinstructions by the power management devices from the control unit. 3.The method as recited in claim 1, wherein said instructions furthercomprising a power limit for each of the consumption units, wherein saidpower limit may be different from unit to unit.
 4. The method as recitedin claim 3, wherein said power limit for each of the consumption unitsis predetermined through a contract by a consumer of the consumptionunit and a power grid operator owning the control unit.
 5. The method asrecited in claim 4, wherein said contract further comprising one or acombination of followings: (a) a price discount for total electricitybill; (b) a credit for consuming a predetermined amount power free or ata discounted rate at low power consumption hours; (c) free or at adiscounted rate for consuming the limited electricity power during peakdemand period.
 6. The method as recited in claim 4, wherein saidcontract may be established by auctioning of the power limits by a powergrid operator to a plurality of consumers of the consumption units. 7.The method as recited in claim 6, wherein said auctioning may beconducted through the communication network and results of auctioningwith regard to power limits of the selected consumption units may bestored in a file storage unit of the control unit automatically.
 8. Themethod as recited in claim 1, wherein said method further comprisingsending a control signal from a controller of the power managementdevice to the power limiter after receiving the instructions by acommunication unit of the power management device from the control unitthrough the communication network.
 9. The method as recited in claim 1,wherein said step of adjusting power consumptions further comprisingswitching off a plurality of preselected appliances and/or reducingpower consumptions for a plurality of preselected appliances.
 10. Themethod as recited in claim 1, wherein said step of adjusting powerconsumptions further comprising receiving inputs from a user through acomputing and communication device by the power management device tomodify the predetermined rules.
 11. A power distribution systemcomprising: (a) a power grid including a control unit for distributingelectricity; (b) a plurality of consumption units connected to the powergrid, wherein each of the consumption units further comprising a powermanagement device; (c) a communication network comprising the controlunit and the power management devices; and (d) a means of reducing powerconsumptions by activating power limiters in said power managementdevices in preselected consumption units.
 12. The system as recited inclaim 11, wherein said control unit further comprising a means ofdetermining supply from a plurality of energy sources and demand fromthe consumption units.
 13. The system as recited in claim 11, whereinsaid control unit further comprising a data file including apredetermined power consumption limit for each of the preselectedconsumption units during peak demand period.
 14. The system as recitedin claim 11, wherein said power management device further comprising acontroller and a communication unit.
 15. The system as recited in claim11, wherein said communication network further comprising an ad hoccommunication network conforming to one or a combination of followingstandards: (a) Bluetooth; (b) ZigBee; and (c) Wi-Fi.
 16. The system asrecited in claim 11, wherein said communication network furthercomprising one or a combination of the follows: (a) a telephone network;(b) the Internet; and (c) a power line communication network.
 17. Thesystem as recited in claim 11, wherein said consumption unit furthercomprising an electricity power meter for measuring output power of atransformer connected to the power grid.
 18. The system as recited inclaim 11, wherein said power limiter may be an AC power limiter.
 19. Thesystem as recited in claim 11, wherein said power limiter may be a DCpower limiter.
 20. The system as recited in claim 19, wherein said DCpower limiter may be connected to a DC/AC converter.